1. Field of the Invention
The present invention relates to a structure obtained by adhering and fixing, in a stacked form, a plurality of thin plate-shaped parts to be used, for example, for an ink-jet printer head and an electronic part.
2. Description of the Related Art
Examples of the ink-jet printer head of the on-demand type are described, for example, in Japanese Patent Application Laid-open No. 62-111758 corresponding to U.S. Pat. Nos. 4,680,595 and 4,730,197, Japanese Patent Application Laid-open No. 10-119263, and Japanese Patent Application Laid-open No. 2002-96478 corresponding to U.S. patent application Publication No. US2002/0036678 A1. As described in these patent documents, a structure is disclosed, in which a jetting pressure-generating member such as a driving piezoelectric element is secured, corresponding to each of portions of a plurality of pressure chambers, to a back surface of a cavity unit composed of a plurality of operating plates retained in an integrated manner by the aid of an adhesive in a stacked state.
The respective operating plates of the cavity unit include a nozzle plate which is provided with a plurality of nozzles, a base plate which is provided with pressure chambers corresponding to the respective nozzles, and a manifold plate which has ink chambers (manifolds) connected to an ink supply source and connected to the pressure chambers. Each of the plates is a thin metal plate having a thickness of about 200 μm or less.
Japanese Patent Application Laid-open No. 2002-96478 discloses the process in which the adhesive is applied to wide width surfaces of the base plate, the spacer plate, and the manifold plate of the cavity unit respectively to overlap and join the plates to one another. In this arrangement, release grooves, which are provided for the adhesive applied on the adhesion surface at positions disposed outer circumferentially as compared with ink flow passages such as the ink manifold, are formed on the wide width surface of each of the plates. Further, air release holes, which are provided to release the air in the plate thickness direction, are formed penetratingly through each of the plates opposed to the release grooves.
In the case of the patent document described above, as shown in FIG. 19, ink flow passages 202, through which the ink flows in the direction from the pressure chambers to the nozzles, are bored in arrays in the long side direction at substantially central portions with respect to the short sides of the plate 201 (illustrated plate is the spacer plate). Ink flow passages 203, through which the ink flows in the direction from the manifold chambers to the pressure chambers, are also bored in arrays in the long side direction at both left and right side portions with respect to the short sides of the plate 201. A plurality of release grooves 204 are formed in parallel to the long side direction of the plate 210 to surround the outer sides of the ink flow passages 202, 203. A large number of release grooves 205 are also formed in parallel to the short sides of each of the plates 201. Accordingly, the effect to release the adhesive is enhanced, and the adhesive is prevented from any inflow into the ink flow passages 202, 203.
However, the stack (cavity unit), which is constructed by laminating the respective plates, receives the pressure exerted from the actuator which is joined on the back surface side thereof, and the respective pressure chambers are expanded and contracted in the long side direction of the plate 201. The pressure chambers are formed in the base plate of the stack, and hence the base plate is also expanded and contracted. The base plate is adhered to the other plates in the stack. Therefore, when the base plate is expanded and contracted, the bending moment tends to be received so that the axis of the cavity unit (plate 201) in the long side direction is bent in the plate thickness direction. Therefore, when the large number of release grooves 205, which are parallel to the short side direction of the plate 201, are formed, the cross sections of the portions of the release grooves 205 parallel to the short side of the plate 201 are decreased. In particular, the plate thickness is thinned, and hence the bending rigidity is decreased with respect to the bending moment in the direction as described above. When the actuator is repeatedly operated, the following first problem has arisen due to the fatigue phenomenon caused by the stress concentration brought about by the stress exerted repeatedly on the portion of the groove parallel to the short side. That is, any crack appears in the plate 201 during the use for a long period of time, the adhesive surface between the respective plates is exfoliated, and any leakage of the ink is apt to occur.
The air release holes are provided in order that the air (bubble), which is caught up in the applied adhesive or by the overlay surfaces of the adjoining plates when the plurality of plates are stacked, pressed, and joined by the aid of the adhesive, is discharged to the outside of the cavity unit via the release grooves. Any excessive amount of the applied adhesive can be also discharged to the outside of the cavity unit via the release grooves and the air release holes during the process in which the overlay surfaces are mutually pressed. Further, the release grooves are not open to the outer circumferential edges of the respective plates. Therefore, when the layer of the applied adhesive is also used as the seal layer, it is possible to avoid the leakage of the ink to the outside of the cavity unit, for example, from the ink flow passages.
However, the following second problem has arisen. That is, when the viscosity of the adhesive is low, then the adhesive overflows to the outside from the through-holes of the plate disposed at the uppermost layer during the operation for pressing and joining the plates, and the adhesive consequently adheres to the pressing and joining apparatus. Therefore, in order to clean and treat the overflow adhesive, it is necessary to frequently perform the maintenance operation for conducting any extra cleaning operation. In other cases, extra time and labor are required, for example, such that the pressing and joining apparatus is laid with a sheet to prevent the adhesion of the adhesive when the pressing and joining operation is performed.
The first and second problems may also arise during the assembling of an electronic part constructed by staking a thin plate formed with a minute pattern onto another thin plate.